1. Field of the Invention
The present invention relates to exposure apparatuses that exposes a substrate via liquid and device manufacturing methods using such exposure apparatuses.
2. Description of the Related Art
There are known exposure apparatuses in which a circuit pattern formed on a reticle is transferred to a wafer by projection exposure using a projection optical system. In recent years, there have been increasing demands for provision of exposure apparatuses having a higher resolution. In response to such demands for a higher resolution, immersion exposure has been attracting attention.
For the purpose of performing immersion exposure in exposure apparatuses, a local-fill method has been proposed, in which liquid is supplied locally between a final surface of the projection optical system and the wafer surface. In a local-fill exposure apparatus, a liquid supplying device supplies liquid through a supply nozzle to a space between the final surface of the projection optical system and the wafer surface, and a liquid collecting device collects the supplied liquid through a collecting nozzle.
In the local-fill method, a central region of the wafer can be exposed in a satisfactory manner without overflow or lack of liquid, whereas exposure on a peripheral region of the wafer may cause some of the liquid to flow off the wafer. To receive the liquid flowing off the wafer, a plate having a surface level substantially the same as that of the wafer (hereinafter referred to as a support plate) is disposed around the wafer. Even with such a support plate, some of liquid may fall into a gap between the wafer and the support plate. If the liquid that has fallen in such a way adheres to a member around the wafer and vaporizes thereon, the vaporization absorbs heat from the member. Consequently, the member may undergo thermal deformation. If a large amount of liquid falls into the gap, the liquid may overflow from the gap and spread inside the exposure apparatus. In such a case, members constituting the exposure apparatus may be corroded. Moreover, the spread liquid vaporizes and thus leaves watermarks. Such watermarks may undesirably cause contamination of members constituting the exposure apparatus.
Therefore, it is necessary to reduce the amount of liquid that falls into the gap and to collect any fallen liquid. To collect the liquid fallen into the gap, configurations in which a liquid collecting unit is disposed in the gap have been disclosed (see International Publication Nos. WO2006/030908 and WO2005/059977, and Japanese Patent Laid-Open Nos. 2004-289127 and 2007-194613).
FIG. 6 is a schematic cross-sectional view showing a part around a wafer 40 in a known immersion exposure apparatus. In FIG. 6, a space between a projection optical system 30 and the wafer 40 is filled with liquid LW. The wafer 40 is supported from the back thereof by a surface 301 of a wafer holder 302, and is tightly secured thereto by being attracted with vacuum. The wafer holder 302 is secured to a top plate 303. A support plate 43 is disposed on the wafer holder 302 in such a manner as to surround the wafer 40 and to have a surface level substantially the same as that of the wafer 40. In this case, the wafer 40 and the support plate 43 are both held on a single wafer holder 302. Further, by giving liquid-repellency to the top surface of the support plate 43, the amount of liquid that remains on the top surface of the support plate 43 after exposing a peripheral region of the wafer 40 is reduced.
A collecting port 304 applies suction to and collects the liquid LW that has fallen into a gutter 300, and is connected to a suction device 308 through a collecting tube 305. The suction device 308 is constituted by a gas-liquid separation device 306 and a pressure reduction source 307. A gap g between the wafer 40 and the support plate 43 is adjusted to be about 0.1 mm to 2 mm.
In the known immersion exposure apparatus, however, the gap g between the wafer 40 and the support plate 43 is large. Therefore, during execution of exposure on a peripheral region of the wafer 40, a large amount of liquid LW falls into the gutter 300. This may cause overflow of the liquid LW from the gap g when a wafer stage 41 is moved and spreading of the overflowed liquid LW over the support plate 43 and the wafer 40, thereby contaminating members constituting the exposure apparatus.
In addition, when the liquid LW fallen into the gutter 300 is collected through the collecting port 304 by applying suction using the suction device 308, vaporization of the liquid LW is promoted. This vaporization absorbs heat from the wafer holder 302 having the liquid LW thereon, whereby the wafer holder 302 and the wafer 40 may become deformed. Consequently, exposure accuracy of the immersion exposure apparatus may be degraded.